The variability of the vertical extent of
the E-layer of the ionosphere (VE) has been examined within the
equatorial ionospheric anomaly region, taken as the difference between 90 km
which is the assumed lower boundary of the layer and the virtual height values
measured with an ionosonde at Ouagadougou in Burkina Faso, West Africa
(geographic lat 12.4°N, long 1.5°W and magnetic dip 5.9°N) for low solar
activity year 1985 and high solar activity year 1990. The vertical extent is a
measure of the vertical altitude of E-region of the ionosphere. The vertical
extent of the E-layer was observed to be high (36-40 km) at sunrise and sunset
while low (18-22 km) at noon for both years. Seasonal variation shows that
vertical extent of E-layer during the solar minimum (maximum) is higher in
September (March) equinox and lower in March (September) equinox. The vertical extent of E-layer has been found to be
an unstable membrane as it varied from hour to hour, day to day, month to month
and season to season in response to the solar activity. The VE is
thicker in the low solar activity (26.30 ± 3.47 km) than the high solar
activity (23.01 ± 2.62 km), which implies that increase/decrease in the solar
activity results in decrease/increase in vertical extent of E-layer. Precisely,
5.4% (35.9%) variation in low (high) solar activity is accounted for by the
variability in solar activity while the remaining percentage may be due to
other factors.

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